In recent years, office buildings and houses have introduced distributed generations, such as solar power generation systems and fuel cell power generation systems. The surplus electric power, remaining after the power generated by the distributed generations is consumed by loads in the houses or buildings, flows back to a distribution system, and is sold to electric power companies. It has been pointed out that if a large number of distributed generations are interconnected to a distribution system in the future, voltage at points of common coupling may deviate from an appropriate voltage range (101±6V, 202±20V) for low-voltage consumers which is defined by a grid-interconnection code, due to backward flow from the distributed generations, simultaneous disconnection of the distributed generations or the like.
In order to prevent voltage from deviating from an appropriate voltage range, there is a known method for controlling voltage at points of common coupling by regulating reactive power to be output by distributed generations. In this method, voltage at connection points is controlled by using, for example, power conditioners included in distributed generations which are capable of regulating reactive power or static var compensators (SVC).
More specifically, distributed generations or SVCs control voltage at connection points by inputting or outputting reactive power according to the line impedance (mainly reactance components) of distribution lines, when the voltage at their own connection points deviate from an appropriate voltage range.
However, when current flowing through distribution lines increases due to an increase of reactive power input or output by distributed generations, SVCs or the like for voltage control, power loss caused in the distribution lines (hereinafter, referred to as distribution loss) also increases, which is a problem.
For example, Patent Literature 1 and Patent Literature 2 disclose techniques for coping with such a problem.